It goes wrong because the include files have changed some day. At my computer at work it still looks ok but not at home. The structure in /usr/include/glib-2.0/gio/gpollableoutputstream.h has changed and that is why I get this error.

So how do I solve this problem?
glib = glib-2.34.2

I tried to unmask gobject-introspection 1.33.14 but failed to do so. The idea was that portage might not complain anymore
Do I really need gobject-introspection?